1. Field of the Invention
This invention in general relates to a process for recovering cobalt catalysts, and more specifically to an improved electrolytic process for recovering and recycling cobalt oxo catalysts.
2. Description of the Prior Art
In the well known oxo process, olefins are hydroformylated by reaction with carbon monoxide and hydrogen, generally charged as syn gas mixtures, in the presence of a cobalt oxo catalyst in dissolved form to form a mixture of oxo aldehydes and alcohols. This oxo reaction is typically carried out at syn gas pressures of from about 1500 to 4500 psig and at temperatures of from about 65.degree. to 230.degree. C. Thereafter, the product mixture containing the alcohols and aldehydes is recovered and can then be treated by known means to hydrogenate the aldehydes to form additional quantities of the corresponding alcohols. These alcohols, in turn, are widely used as chemical intermediates in the manufacture of plasticizers, detergents, solvents and the like.
Prior to the hydrogenation step, the crude oxo reaction effluent, which contains dissolved cobalt catalysts, the aldehyde and alcohol products and reaction by-products together with any metallic contaminants, is generally treated to remove the dissolved cobalt catalyst, which then for reasons of economy must be recycled to the oxo reactor.
A wide variety of catalysts recovery/recycle processes have therefore been developed. In co-pending applications "Improved Process for Recovery of Cobalt Catalysts" Ser. No. 333,734, filed Dec. 23, 1981 and "Improved Oxidative Recovery of Cobalt Oxo Catalysts" Ser. No. 333,693 filed Dec. 23, 1981 processes are disclosed in which aqueous solutions of a tetracarbonylcobaltate metal salt as contacted with an oxygen containing gas, optionally in the presence of gaseous carbon monoxide and optionally also in the presence of an organic solvent for dicobalt octacarbonyl or in the presence of an olefinic extractant for dicobalt octacarbonyl, to oxidize the tetracarbonylcobaltate anion to dicobalt octacarbonyl which is then recovered in liquid phase. An organic phase containing the dicobalt octacarbonyl can be recycled to olefin hydroformylation zone to provide at least a portion of the catalyst feed thereto. The discussion of other prior art processes for removal and recycle of cobalt catalysts from crude oxo product effluent in each of the above-referenced applications, Ser. Nos. 333,693 and 333,734, both filed Dec. 23, 1983, is hereby incorporated by reference.
The electro-potential of Co(CO).sub.4 H in glacial acetic acid has been determined by W. Hieber and W. Hubel, Zeitchr. Elektrochem., 57, No. 4, pp. 235-243 (1953). The oxidation-reduction potential of the system EQU 2[Co(CO).sub.4 ].sup.- .revreaction.[Co(CO).sub.4 ].sub.2 +2e.sup.-
has also been determined by W. Hieber and W. Hubel, Z. Naturforsch. 7b, 323-324 (1952) to be E.sub.o =-0.4 V, at 20.degree. C. as measured on a platinum electrode (against calomel) and referred to a normal hydrogen electrode.